Amphiphilic block copolymers are well known. The majority of amphiphilic polymers are diblock copolymers that are soluble in water. These diblock polymers are used to thicken aqueous solutions and form viscoelastic gels, such as those described in U.S. Pat. Nos. 6,506,837; 6,437,040, and US Patent application 2003/0162896.
Amphiphilic triblock copolymers known commercially as Pluronics are also well described in the literature. These triblock copolymers can contain hydrophilic endblocks and a hydrophobic midblock or vice versa. The hydrophilic block segment is confined to polyethylene oxide (PEO) homopolymer. The triblocks containing hydrophilic endblocks are soluble in water. The triblocks containing hydrophobic endblocks will be insoluble in water.
Amphiphilic diblock polymers may be formed using stable free radical chemistry, as described in U.S. Pat. No. 6,111,025. These polymers are limited to diblock structures, and furthermore describe the use of TEMPO-based nitroxide derivatives for the synthesis of the corresponding block copolymers. This class of free radical control agent [such as (2′,2′,6′,6′-tetramethyl-1′-piperidyloxy-)methylbenzene mentioned in Macromolecules 1996, 29, pages 5245-5254] control only the polymerizations of styrene and styrenic derivatives and are not suited to the controlled polymerization of acrylics. U.S. Pat. No. 6,767,968 describes the use of living-type or semi-living type free radical polymerization to form copolymers having a random block with both a hydrophobic and hydrophilic monomer units. These block polymers are soluble in water or alcohol.
Arkema patent application US 2006052545 describes a diblock copolymer adhesive formed by a controlled radical polymerization that is capable of absorbing water and providing adhesion under humid conditions. This polymer could be water soluble.
Amphiphilic block polymers for use as additives and thickeners in oil-based compositions are described in WO 05/056739.
Hydrogels are typically polymeric materials, which are capable of absorbing aqueous fluids. Hydrogels are generally hydrophilic polymeric materials that have been chemically crosslinked to remain insoluble in water. Hydrogels are often used in wound care, in hygiene articles, in filtration aids, as flexible cushioning materials, as control-release agents, and for the adsorption of aqueous-based fluids.
There is a need for an amphiphilic polymeric material that has excellent water absorption and permeation and is formed without covalent crosslinks. The absence of covalent crosslinks inherently provides ease of processing (by solvent casting, spin coating, spray coating, melt processing, melt blending, etc.) not present in the covalently crosslinked systems. One use of these materials would be as a hydrogel. Furthermore there is a need to be able to control the water absorption/permeability of the composite as well as the physical and mechanical properties, for example, ranging from a tough thermoplastic type material, for applications such as membranes to tacky rubbers for applications such as pressure sensitive adhesives.
Surprisingly it has been found that a class of multiblock copolymers having a general structure of a hydrophilic middle block and hydrophobic outer blocks can be made by a controlled radical polymerization method to form an amphiphilic copolymer with tailored properties. Furthermore, the physical properties, mechanical properties and the water absorption/transmission properties of the amphiphilic triblock copolymer can be tailored by adjusting the levels and types of monomers in each of the block segments, as well as by adjusting the size and ratio of the blocks. Some of the properties that can be optimized include the level of water or other fluids absorbed and transmitted, gel strength, and other physical and mechanical properties (e.g., materials can range from a brittle thermoplastic to a tacky rubber).